Accessibility and transport infrastructure improvement assessment: The role of borders and multilateral resistance

The market potential indicator is a commonly used tool in transport planning for evaluating the potential economic effects derived from improvements in transport infrastructures. The general assumption is that exports from a given region will rise with increased accessibility, thus benefiting economic activities. However, the specification of the market potential model is typically very simple and ignores both the impact of competing rivals and the role of international borders, which leads to unrealistic results. Spatial interaction models on bilateral trade have already proved that international trade is affected by multilateral resistance, borders, adjacency, language or currency. Nevertheless, apart from some recent analyses that simply calibrate the distance decay parameter from trade datasets, these variables have hardly been integrated into research on market potential. This paper sets out to demonstrate that more realistic results are obtained by calibrating the distance-decay parameter and introducing the impact of competing rivals and border effects into the market potential formulation. The proposed model is then applied to the assessment of the accessibility impacts of new road transport infrastructure in the European Union between 2001 and 2012, which shows that the greatest improvements in accessibility were experienced by peripheral countries with high road infrastructure investment.     

Evolving competition between Hong Kong and Shenzhen ports

Shenzhen Port (SZP), once a negligible local port, has risen dramatically to a world-leading container port and an “equal” player with Hong Kong Port (HKP). Will this market share reallocation continue, or will equilibrium be eventually realized for HKP to prosper continuously? We examine the relationship between these two ports to answer this question. We propose a new transformation method to describe the growth of container cargo transport demand, define the quantitative measures of the competition relationship and port competitiveness, and present a rigorous analytical framework with econometric tests and models to understand the true relationship between HKP and SZP. Direct empirical tests suggest that SZP complements HKP; however, the two ports exhibit strong competition when the effect of demand growth is excluded. Considering transshipment separately, we find that the impact of SZP on HKP is negative in transshipment but complementary in direct shipment. We may conclude that HKP does not affect SZP, whereas SZP has competitive power over HKP. These results are consistent with the findings of some previous theoretical studies.     

汽油机活塞组—气缸套整体耦合传热模型及应用

采用直接耦合的有限元分析方法对一汽油机的活塞组—气缸套系统的瞬态传热过程进行了研究。通过将润滑油膜假设为一维热阻,建立了活塞组—气缸套整体耦合系统的三维传热模型,应用所开发的三维流体动压润滑分析程序对活塞环组沿周向瞬时变化的油膜厚度进行了计算与分析。以LJ377MV汽油机活塞组—气缸套零部件为对象进行了应用研究,获得了更为清晰的多部件间的相互传热关系。     

一个应用复合箱体结构传动箱的柴油发电机组设计

因运载车辆或其它条件限制,在某些情况下,柴油发电机组设计中需将发电机布置在柴油发动机的侧面,以减小机组在长度方向的尺寸。本文对该种布置方式的力学特性进行了分析,并从传动齿轮箱设计和柴油发电机组结构总成方面提出了合理的设计方案,产品经运行效果良好,证明具有使用价值。     

整体式桥台的箱梁剪滞效应分析

针对整体式桥台的箱梁固有的力学特性,建立有限元模型,对其在不同荷载作用下剪滞系数的横向和纵向分布规律进行研究,并将结果与普通简支箱梁进行比较。通过有机玻璃模型试验验证了有限元建模分析的可行性、准确性,同时作了参数分析,提出了可供工程设计参考的实用剪滞系数计算表。分析结果表明:该类箱梁剪滞分布与普通简支箱梁的不同主要在于桥台附近截面出现了负剪滞现象;整体式桥台的纵向抗弯刚度、主梁宽跨比、宽高比及不同荷载形式等是影响该类桥梁剪滞系数的主要因素。     

水位下降对边(滑)坡稳定性的影响

通过PLAXIS有限元程序对一边坡算例进行分析,根据实际工程的需要选择理想弹塑性模型和莫尔-库仑屈服准则进行数值模拟,并对比分析了土体分别设置为排水条件和不排水条件时的情况。计算结果表明,当土体设置为排水条件时,在库水水位下降过程中,安全系数随水位的下降逐渐减小,但当水位下降了20 m以后,由于孔隙水压力给滑面提供了竖直方向的作用力,随着水位的继续下降安全系数反而略有上升。当土体设置为不排水条件时,坡体内产生的超孔隙水压力对边坡安全系数的降低更为明显。考虑坡体内超孔隙水压力时安全系数的计算结果比不考虑坡体内超孔隙水压力时的计算结果低10%左右,因此实际工程中应该充分考虑超孔隙水压力的积累和消散,并根据"最不利水位"所对应的安全系数进行校核。在计算过程中PLAXIS程序能较好地模拟水位下降引起的渗流作用对边(滑)坡稳定性的影响。     

桥梁结构地震碰撞效应及防落梁措施研究现状

介绍了桥梁结构地震碰撞效应及防落梁措施方面的一些近期进展。在介绍了接触碰撞问题的计算理论及分析方法的基础上,对地震作用下相邻桥梁结构间碰撞效应的理论以及试验研究进展进行了回顾和总结;并针对地震中桥梁上部结构发生落梁的问题,介绍了减轻相邻梁体间碰撞的措施、桥梁伸缩缝处的支承宽度、纵向限位器的设计方法、横向抗震挡块的设计方法等研究方面的进展,分析了各国抗震设计规范对桥梁伸缩缝处支承宽度的规定,同时指出目前我国在这方面研究的欠缺。     

基于能量变分原理的薄壁箱梁自振特性分析

以能量变分原理为基础,综合考虑剪力滞后效应、剪切变形和转动惯量的影响,推导出箱形截面梁的控制微分方程和相应的自然边界条件,据此获得几种常用边界条件(简支、悬臂、连续、两端固支)的固有频率方程,提出一种能对工程中常用矩形薄壁箱梁自振特性进行分析的方法。通过算例将解析解与板壳有限元结果进行了比较,证明了该方法的有效性,所得公式比以往剪滞理论有一定发展,且为箱形梁桥动力特性的进一步研究奠定了理论基础。     

汽车上的电磁干扰及抑制措施

电磁干扰以多种方式存在于汽车内部，这些干扰对车载电子装置及无线电接收设备会产生不同程度的影响。就车内电气部件所产生的电磁干扰及其形成机理提炼出来进行分析，并提出了有效的抑制措施。     

载货汽车驾驶室乘坐舒适性研究

通过计算机仿真模拟了在路面随机输入下驾驶室底板的振动响应;利用Nastran软件对车身的有限元模型进行模态抽取,建立了刚弹耦合模型;对多刚体模型、刚弹耦合振动模型的计算结果与试验进行了对比,验证了模型的正确性;以驾驶室悬置的弹簧刚度、减振器阻尼为影响因素,通过虚拟DOE正交试验分析,显著改善了驾驶室的乘坐舒适性。